Composite roof deck assemblies are disclosed in U.S. Pat. No. 4,601,151; U.S. Pat. No. 4,736,561; U.S. Pat. No. 4,707,961 and U.S. Pat. No. 4,783,942.
U.S. Pat. No. 4,601,151 discloses a roof system comprising a sheet of corrugated material having ridges and a rigid substrate, such as a mineral board, fastened to the upper ridges of the corrugated sheet. The corrugated sheet is welded to roof purlins. The mineral board, on the other hand, is fastened to the corrugations of the corrugated sheet by threaded fasteners which extend through the mineral board and through the ridges to form a truss -like structure that spans between the roof purlins.
When an insulated roof is desired, insulation is interposed between the mineral board and the corrugated sheet. As the insulation thickness increases the length of the threaded fasteners increases, creating potential rotation and bending problems for the fasteners. As a result the thickness of the insulation is limited by the threaded fastener length. Additionally, since fasteners typically extend all the way through the roofing layers from the exterior of the roof to the interior supporting structure of the roof, thermal shorts are created between the exterior of the roof and the interior of the roof, which is undesirable in extremely cold climates.
A roof system with improved insulation is desired which will eliminate the thermal shorts by providing a staggered anchoring system and, subsequently, shorter threaded fastener lengths thereby alleviating potential rotation and bending problems.